Electrical current collecting devices

ABSTRACT

An electrical current-collecting device for passing high currents between relatively fast moving conductors is in the form of a circular brush having projecting conducting bristles and mounted on a spindle about which it is rotated with the bristles in contact with a moving conductor so that the relative speed between the conductor and the bristles is relatively small and good electrical conduction is achieved. The current may then be passed on to a second, normally stationary, conductor through the spindle made of conducting material and much smaller in diameter than the brush so that contact with the second conductor can be made at relatively low speed.

atent [191' ELECTRICAL CURRENT COLLECTING navrcas Inventor: James JohnBates, Shrivenham,

England Assignee: National Research Development Corporation, London,England Filed: Nov. 19, 1971 Appl. No; 200,550

Foreign Application Priority Data Nov. 20, 1970 Great Britain.. 55,266/70 References Cited UNITED STATES PATENTS 12/1970 Bates 318/1383,648,088 3/1972 Wilkin 310/219 2,785,364 3/1957 Lane 3,341,726 9/1967Brinster 3,382,387 5/1968 Marshall 1,670,030 5/1928 Fynn 3,375,4793/1968 Lowe 310/232 Primary ExaminerR. Skudy Attorney- (iushman, Darby &Cushman [57] ABSTRACT An electrical current-collecting device forpassing high currents between relatively fast moving conductors is inthe form of a circular brush having projecting conducting bristles andmounted on a spindle about which it is rotated with the bristles incontact with a moving conductor so that the relative speed between theconductor and the bristles is relatively small and good electricalconduction is achieved. The current may then be passed on to a second,nonnally stationary, conductor through the spindle made of conductingmaterial and much smaller in diameter than the brush so that contactwith the second conductor can be made at relatively low speed.

9 Claims, 12 Drawing Figures PAIENImnmsoma v 3,769,535

SHEET REF 3 PATENTEDHBT30 m 3.769.535

SHEET 3 OF 3 1 ELECTRICAL CURRENT COLLECTING DEVICES This inventionrelates to electric current-collecting devices.

Electric currents have been collected from a rotary conductor by meansof a stationary brush, but the relative movement of the brush andconductor leads to wear, which is a particularly deleterious when highspeed rotation is involved as would be the case in a largeturbo-alternator. In addition, such an arrangement may have aconsiderable voltage drop between the conductor and the brush, and sucha voltage drop may not be tolerable, for example in a homopolar machinewhich generates at a low voltage so that a very heavy current must becollected.

Electric currents have also been collected by a freely rotating wheelsuch as that described in U.S. Pat. No. 3,544,868 but at high speedssuch a wheel may not provide satisfactory contact due to small particlestrapped between the wheel and the surface on which it runs.

According to the invention, an electrical currentcollecting device forconducting electrical current between first and second relativelymovable conductors, said device comprising a circular brush having aplurality of projecting conducting bristles and arranged to be rotatablewith the ends of the bristles in electrical contact with the said firstconductor so that the relative velocity between thefree ends of thebristles and the first conductor is much smaller than the rate ofrelative movement between said first and second conductors, the devicealso having a contactor for making an electrical connection with thesaid second conductor at a relative velocity substantially smaller thanthe relative velocity between the first and second conductors.Preferably the bristles of the brush project radially. The said firstconductor may be a fixed linear conductor, when the circular brush mayrotate about a spindle perpendicular to the linear conductor, thespindle being moved in the direction of the conductor. However,'moreusually the said first conductor will be a rotary conductor rotatingabout an axis either parallel to the axis of rotation of the circularbrush, when contact may be made over the annular surfaces of the brushand rotary conductor, or perpendicular to the axis of rotation of thebrush, when the annular surface of the brush may make contact with aflat face of the conductor.

In a particularly advantageous embodiment of the invention, the circularbrush is mounted on a contactor comprising an electrically conductingspindle of substantially smaller diameter than the circular brush andcontact is made between the spindle and a second conductor comprising astationary brush, the peripheral speed of the spindlebeing'substantially lower than that of the circular brush so thatrubbing wear is small. If necessary the spindle may be arranged to makecontact withthe circular brush of a similar current-collecting deviceand further brushes and spindles sequentially so that the peripheralspeed of the last spindle in the train is sufficiently low to allowcontact with a stationary brush at acceptably low rubbing speed.

Alternatively the circular brush may be mounted on a conducting spindleone end of which is immersed in a container of electrically conductingfluid such as mercury or a mass of electrically conductive powder whichmay possibly be fluidised by the passage through it of a current of air,and static electrical contact can then be made between the container anda second electrical conductor.

The circular brush and the first conductor, when rotary, are preferablyeach independently driven, either by separate servo-controlled electricmotors or by gearing. Alternatively, thecircular brush may be driven byfrictional engagement with the first conductor. The rotary firstconductor may be a slip ring, when use of metal bristles for the rotarybrush is advantageous, or may be a commutator when use of carbon fibrebristles is preferable to give a more progressive change in resistanceas the brush moves from segment to segment.

, While the electrical contact between the bristles of the circularbrush and the first conductor is satisfactory if the brush is rotatingat sufficiently high speed for the bristles to be pressed against thefirst conductor by centrifugal force, at low speeds there may beinsufficient centrifugal force to make good contact. The bristles cannotbe forced against the conductor by spring pressure since excessivedistortion would result. It may therefore be advantageous to use acircular brush according to the invention in conjunction with a solidcircular brush or wheel arranged so that the wheel can act as aconductor at low speeds and the bristles can act as a conductor at highspeeds. Such an arrangement may be used when it is desired to pass highcurrents between relatively moving parts when the rate of relativemovement varies over a wide range. The arrangement is particularlyadvantageous since at high speed a wheel may not provide satisfactorycontact as very small particles may be trapped between the wheel and thesurface on which it runs, but the wire brush will provide protectionagainst such loss of contact. In addition the wheel may be pressedagainst the first conductor with such force that it may act as africtional drive by which the wheel and brush may be rotated.

An important feature of the invention is that it may be applied to acascaded homopolar machine such as a multi-disc type machine whensuccessive discs may be connected by a current collector in accordancewith the invention. Similarly a current-collecting device may be used ina segmented type of cascaded homopolar machine and such acurrent-collecting device is particularly useful for homopolar machinesusing superconducting field coils.

Another important feature of the invention is that the device may beused in a dynamo-electric machine to provide a commutation arrangementin which a commutator having segments of conducting material separatedby segments of insulating material is contacted by a circular brush orbrushes as contact members. The

machine may comprise thyristor-assisted commutation arrangements such asdescribed, for example, in U.S. Pat. No. 3,453,513.

The invention will now be described by way of example only withreference to the drawings filed with this specification in which:

FIGS. 1 and 2 illustrate two embodiments of a current collectoraccording to the invention;

FIG. 3 illustrates a current collector in conjunction with a wheel-typecurrent collector;

FIG. 4 illustrates a gear-driven current collector;

FIG. 5 illustrates a train of current collectors;

FIG. 6 illustrates current collection from a linear conductor;

FIGS. 7 and 8 a,b illustrate schematically useof current collectors inmultiple-disc and segmented-disc type cascaded homopolar machinesrespectively;

FIG. 9a illustrates schematically use of a current collector to transfercurrent between a slip ring and a commutator; and

FIGS. 9b and 9c illustrate sections through the slip ring and commutatorof FIG. 9a.

In FIG. 1, a mass of fine copper bristles forming a circular brush 10,project radially from and are clamped between two metal discs 12, 14secured on a metal spindle 16 by two clamping members 18 of which onlyone can be seenLThe brush is in peripheral contact 4 oxidation. Thebrush 28 is in. contact with the 'face of a disc-shaped currentgenerator 34 and close to the rim thereof. The collector 34 is rotatedabout a spindle 36 with a first condutor, in this case the'rim 19 of adiscshaped current generator 20 which is clamped to a spindle 22 whichis rotated relative to a magnetic field, produced by means notillustrated, so as to generate a voltage radially of the disc 20. Thespindle 16 is rotated by means of an electric motor 24, and stationarycontacts 26 are arranged so as to be in contact with the spindle 16;thecontacts 26 here being the second conductor.

' The motor 24 is driven so as to rotate the spindle 16 so that theperipheral speeds of the rim 19 and the the total peripheral area of thebrush 10-is approximately 9 square inches. At any instant the actualbrush area in contact with the rim 19, which area will depend upon theextent to .which the periphery of the brush 10 is slightly flattened bycontact with the rim 19, will be only a fraction of this but due to therotation of the brush 10, the contact points will be continuouslychanging so that the effective peripheral area of sucha brush will beequivalent to the 9 square inches of total peripheral area. i

r 'The difference between the diameters of the disc 20, the brush 10 andthe spindle 16 maybe such that the peripheral speed of spindle 16 is lowenough for stationary contacts 26 to collect current from it without anunacceptable voltage drop and without an excessive rate of wear. Forexample ifthe disc 20 were the disc of a homopolar machine, 6 feetindiameter and run at 100 rpm, with a peripheral speed of over 1,800 feetper minute, a 6 inch diameter brush 10 could be driven at 1,200 rpm andthe spindle 16 could be 1 inch diameter so that its peripheral speedwould be 300 feet per minute. Due to the deflection of the bristles ofthe brush 10 by contact with the rim 19, by say one-eighth inch, therelative velocity of the brush l0 and rim 19 might be of the order 60feet per minute which would provide a desirable sliding and cleaningaction without excessive wear.

FIG. 2 illustrates schematically an alternative construction in which abrush 28, of the same general kind as that referenced 10 in FIG. 1,rotates on a vertical metal spindle 30, -the lower end of which passesthrough a seal into a closed conductive pot32, containing mercury inwhich the spindle 30 is immersed to make end and peripheral contact. Theseal is of conventional kind and preferably there should be the usualprovision for reducing deterioration of the mercury by by means notshown and the brush 28 is rotated by means of frictional contact withthe generator 34, current passing from the generator 34 through thebrush 28 and spindle 30 to the pot 32 and being collected by a contactindicated by reference 38.

In. FIG. 3, abrush 40 having bristles 42 is mounted on a spindle 44which also carries a solid metal wheel 46 the diameter of which isslightly less than the peripheral diameter of the bristles 42. Thebristles 42 and wheel 46 are in contact with a'rotating disc 48 formingthe first conductor.v The spindle 44 projects into a conductive pot 50whichcontains mercury and is in contact with a second conductor asindicated by reference 52. Pressure is applied to the spindle in thedirection of the arrow P so that the wheel 46 presses against the disc48 and as the disc rotates, provides friction drive for the-spindle 44and brush 40.

When the spindle 44 is rotated at low speeds, current passes from thedisc 48 to the second conductor 52 through the wheel 46, because thebristles 42 are not in good contact with the disc 48. However at highspeeds the bristles 42 are pressed against the disc 48 by centrifugalforce and good contact is made so that current can pass through both thebrush 40 and the wheel 46. If contact between the brush 46 and disc 48is momentarily interrupted by particles trapped between them, as mayeasily occur at high speed, then the cur.- rent passes through the brush40 alone.

' In FIG. 4, a disc-shaped current generator 54, from which current mustbe collected at the periphery, is fixed to a spindle 56 rotated by amotor 58. A circular brush 60 is attached to a spindle 62 arranged sothat the bristles 64 of the brush 60 are in peripheral contact with thedisc 54. The spindle 56 and 62 are parallel and carry gear wheels 66 and68 respectively'meshing with idler gear 70 and 72, the gear ratios beingarranged so that the peripheral speeds of the disc 54 and bristles 64are substantially equal.

FIG. 5 illustrates a very high speed disc-shaped current generator 74mounted on a spindle 76 rotated by a motor 78. The periphery of the disc74 is in contact with the bristles of a circular brush 80 mounted on aspindle 82 rotated by a motor 84. Further brushes 86, 92 are mounted onspindles 88, 94 rotated by motors 90, 96 and the speeds of the motors78, 84, and 96 are arranged so that the velocities of the periphery ofthe bristles of brushes 80, 86 and 92 are substantially equal to theperipheral velocities of the disc 74 and the spindles 82 and 88respectively. The velocity of spindle 94, the last spindle in the train,is very much slower than the velocity of disc 74 and contact can be madeby a stationary brush 98 with acceptably low rubbing wear, the brush 98here being the second conductor.

In FIG. 6 a circular brush 100 rotates about a spindle 102, the brush100 being in peripheral contact with a fixed conductor rail 104 formingthe first conductor. The side of the rail 104 adjacent to the brush 100is grooved as indicated by reference 106 to provide the equivalent ofteeth. The spindle 102 is moved in the direction of the arrow and thebrush 100 engages the grooves 106 ,so that the brush 100 is rotated byfrictional force. Such an arrangement could be used to conduct electriccurrent from a conductor rail or wire to an electric vehicle, as on anelectric tramway or railway.

It will be appreciated that arrangements for driving the currentcollectors and making contact with the second conductor in FIGS. 1 to'6are interchangeable. For example the train of current collectors in FIG.5 may be driven by gearing from a single motor, and in FIG. 3 theconducting pot may be replaced by a stationary brush.

In FIG. 7 a series of conductive discs 108 A, B, C, D are attached to aninsulating cylinder 110 which is attached toa rotatable shaft 112, toform a cascaded homopolar machine. The disc 108B has an axial extensionwith a radial rim 114, and a current-collecting device 116 is arrangedradially between discs 108A and 108B. The current-collecting device 116hasan outer large diameter brush 118 in contact with a face of disc 108Anear its periphery and an inner smalldiameter brush 120 in contact withthe radial rim 114 of disc 108B. The brushes 118, 120 are carried on aspindle 122 supported in bearings not illustrated, and which rotates inthe direction indicated by the arrow; the diameters of the two brusheson the spindle 122 are in the same ratio as the radii of contact withthe discs 108A, 108B.

Similarly, current collecting devices 124, 126 are arranged betweendiscs 108B, 108C and 108C, 108D respectively. The brush 128 of an inputcurrent collecting device 130 is in contact with a part of disc 108Aradially close to the shaft 112 and the brush 132 of an outputcurrent-collecting device 134 is in contact with the outer part of disc108D, current-collecting devices 130 and 134 being of the mercury pottype already described with reference to FIG. 2.

In operation the current-collecting devices 118, 124, I26, 130 and 134are all driven by friction with the discs 108 as the homopolar machinerotates. A current can be considered to flow from an external circuit todisc 108A from which it passes to current-collecting device 118, disc108B, current-collecting device 124 and so on, the induced EMF buildingup between succes'sive discs, andback to the external circuit throughthe current-collecting device 134.

FIG. 8a shows part of a segmented-disc type homopolar machine and FIG.8b illustrates a section through the disc of FIG; 8a. The disc 136 ismade up of conducting sectors 136A, 1368 and so on separated byinsulating gaps 138, the disc rotating on a shaft 140. A number ofcurrent-collecting devices equal to the number of sectors less one arearranged radially. One current-collecting device 142 is shown, with alarge diameter rotary brush 144 in contact with the outer part of asector 136A and a small diameter rotary brush 146 in contact with theinner part of an adjacent sector 136B, the brushes 144, 146 rotating ona radial spindle 148; the insulating gaps 138 are inclined to the radialdirection sufficiently to allow such an arrangement. The ratio of thediameters of the two rotary brushes 144, 146 is equal to the ratio ofthe radii of the two circles of contact on the disc 136; in order tokeep the rotary brush spindle 148 perpendicular to the axis of the disc136 while leaving room to accommodate the larger outer rotary brush 144,the disc 136 is either stepped (not shown) or tapered so that it isconsiderably thinner at its periphery where it is engaged by theradially outer brush (see FIG. 8b); or the disc may be formed hollow, ieas a shallow cone. A succession of such spindles and rotary brushes upto the number of sectors less one forms stationary connections which puteach of the rotary sectors 136A, 1363 and so on in series with the nextone in a direction in which the EMFs induced will add up. Individualinput and output rotary brushes (not shown) are provided correspondingto the last sector. The current collecting devices are driven by meansof gears 150, 152 connected to the shaft 140.

In a further arrangement the sectored disc of FIG. 8 may be only one ofseveral discs on a shaft, the connections between the discs also beingmade by current collectors.

In a more practical application of the invention to such homopolarmachine as shown in FIGS. 8a and 8b a more complicated arrangement ofwire brushes may be used to prevent the shorting out of adjacentsegments as the brush crosses from one segment to another.

' In FIG. 9a a commutator 154 and a slip ring 156 are arrangedconcentric with the shaft 158 of a rotary electric machine. Thecommutator 154 comprises conducting segments 154A, B, C etc as shown inFIG. 9b each connected to the armature windings on the stator (notshown) by electrical connections 160A, B, C etc. The slip ring, shown insection in FIG. 9c, is connected through connection 162 to one of theelectrical supply terminals of the machine.

The rotor shaft 158 carries a cross-piece 164 which rotates with theshaft 158 and has a bore 166 containing'a bearing 168 and a rubber bush170 which supports a spindle 172. At one end the spindle 172 carries acircular brush 174 having bristles in contact with the inside surface ofthe commutator 154, and a wheel 176 also in contact with the commutator.Similarly a brush 178 and wheel 180 at the other end of the spindle 172are in contact with the slip ring 156. The spindle 172 can rotate freelyin the bearing 168 and the rubber bush 170 ensures good contact with thecommutator 154 and slip" ring 156.

As the shaft 158 rotates, the slip ring 156 is connected through thespindle 172 to each segment of the commutator 154 in turn. Since thereis no sliding contact there is no possibility of the formation ofconductive tracks between the commutator segments as would occur withcarbon brushes. Thus it is possible to considerably increase the voltageapplied to the armature winding of the machine without danger offlashover between adjacent commutator segments.

It will be appreciated that it is not essential to have both a circularbrush and a wheel in contact with the commutator and slip ring. It maybe possible, for example, to use a circular brush only in contact withthe commutator and a solid Wheel only in contact with the slip ring.

FIG. 9 is intended to indicate in a general way the use of acurrent-collecting device according to the invention in a rotaryelectrical machine. The invention may also be applied to othersituations such as those described in more detail in US. Pat. No.3,544,808.

The brushes so far described have the bristles projecting radially andpresenting a cylindrical surface. For some purposes it may be possibleor convenient to use an alternative construction in which the bristlesaround the rim of a brush disc project axially and promeans forconducting an electrical current between said conductors comprising atleast one circular brush having a plurality of projecting conductingbristles and having driving means wherein said circular brush is drivenwith the ends of the bristles in electrical contact with said firstconductor at such a speed that the relative velocity between the freeends of the bristles and the first conductor is small compared with therate of movement of the first conductor and having contact means formaking an electrical connection with said second conductor.

2. An electrical device according to claim 1 in which any circular brushis mounted on a conducting spindle of substantially smaller diameterthan the brush, the spindle comprising the contact means for makingelectrical contact with the said second conductor.

3. An electrical device according to claim 2 in which a solid wheel typeof current collector of diameter slightly less than the diameter acrossthe outer ends of the bristles of the circular brush is mounted on thespindle and makes electrical contact with the same conductor as thecircular brush.

I between the first and second conductors there is at least one furtherdevice.

8. An electrical device according to claim 1 incorporated in a rotatableelectrical machine.

9. An electrical device according to claim 1 in which the first andsecond conductors are each in contact with a circular brush having aplurality of projecting conducting bristles, whereby an electricalcurrent can be conducted between said first and second conductOl'S.

1. An electrical device comprising first and second conductors at leastthe first of which is movable, and means for conducting an electricalcurrent between said conductors comprising at least one circular brushhaving a plurality of projecting conducting bristles and having drivingmeans wherein said circular brush is driven with the ends of thebristles in electrical contact with said first conductor at such a speedthat the relative velocity between the free ends of the bristles and thefirst conductor is small compared with the rate of movement of the firstconductor and having contact means for making an electrical connectionwith said second conductor.
 2. An electrical device according to claim 1in which any circular brush is mounted on a conducting spindle ofsubstantially smaller diameter than the brush, the spindle comprisingthe contact means for making electrical contact with the said secondconductor.
 3. An electrical device according to claim 2 in which a solidwheel type of current collector of diameter slightly less than thediameter across the outer ends of the bristles of the circular brush ismounted on the spindle and makes electrical contact with the sameconductor as the circular brush.
 4. An electrical device according toclaim 1 in which any circular brush and the conductor with which it isin electrical contact are independently driven.
 5. An electrical deviceaccording to claim 1 in which any circular brush is driven by mechanicalgearing with the drive means of the conductor with which said circularbrush is in contact.
 6. An electrical device according to claim 1 inwhich the first conductor is grooved so as to drive positively thecircular brush with which it is in contact.
 7. An electrical deviceaccording to claim 1 in which between the first and second conductorsthere is at least one further device.
 8. An electrical device accordingto claim 1 incorporated in a rotatable electrical machine.
 9. Anelectrical device according to claim 1 in which the first and secondconductors are each in contact with a circular brush having a pluralityof projecting conducting bristles, whereby an electrical current can beconducted between said first and second conductors.